1. Field of the Invention
The present invention relates to the field of location and plotting of a point or a set of points.
The invention is more particularly directed to a method and a device for determination and plotting with enhanced accuracy and for the purpose of subsequent reproduction if necessary, of graphs, curves, time-dependent variations in displacement and more generally of any patterns having one, two or even three dimensions, for checking signatures, recording "know-how" or measuring distances, as well as other applications which will be indicated in greater detail in the following specification.
2. Description of the Prior Art
A number of different solutions have already been proposed for computer entry or acquisition of cartesian coordinates in real time for the purpose of display or subsequent processing.
Consideration has thus been given to the use of a device in which conductor wires are arranged in webs or parallel arrays corresponding to the XY cartesian coordinates and embedded in a suitable material, location of the point or set of points being performed by means of a sensing pen or electromagnetic radiation emitter.
Similarly, it has been propsed to form each web of XY coordinates by means of a parallel beam of laser light rays.
Use has already been made of supports representing a variable resistance, determination of the coordinates of each point being performed by means of the electric contact produced by a pen.
Other devices consist of a potentiometer equipped with mechanical arms. As an alternative to orthonormal arms, the devices can be adapted to satisfy polar coordinates.
Another device proposed in the prior art consists of a matrix of phototransistors or of a web of optical threads. In this device, the pencil used for determining the position of the point to be located was provided with sensing devices.
There has also been developed an electroacoustic system mounted on metal supports for determining the time of propagation of shock waves by utilizing the piezoelectric properties of a crystal.
In U.S. Pat. No. 3,665,608, there was described a device for locating the position of a point, comprising a stylus inserted in two superposed cylinders. Two threads are fixed around the cylinders whilst the other end of the threads are wound around two drums. When the stylus is moved, one drum or both drums consequently rotate in order to accommodate the change in length of the threads. The angular position of each drum is measured by so-called angle transducers, the output of which is coupled with a computer in order to obtain the position of the stylus. This patent is therefore based on the principle of determination of angles and not determination of distances.
In German Pat. No. 2,245,178, a device was proposed for transmitting arbitrary movements in order to produce a signal which is representative of the three-dimensional movement of a point. This device comprises three elements around which are coiled threads connected at one end to a pencil. Traction means apply constant tension to the threads, with the result that the output signal of the converter is representative of the displacement of the thread with respect to the traction means. Measurement of length of the threads is therefore performed continuously by potentiometer.
Finally, it has been proposed to employ an ultrasonic-wave emitting pen, sensors being fixed on the edges of the device employed.
The solutions mentioned in the foregoing have all led to generally positive results in regard to the accuracy achieved in determinations of coordinates although the degree of accuracy varies considerably from one type of apparatus to another.
However, it will readily be apparent that these solutions make it necessary to provide cumbersome equipment which is costly to produce in most instances, particularly in the case of the most accurate types of apparatus.
Furthermore, such solutions involve the use of means which lack flexibility of operation and are often incompatible with high-speed plotting operations in which accurate performance has to be maintained.